1. Field of the Invention
The present invention relates to a method for regulating a generator and, more particularly, to a method of regulating a claw pole generator driven by an internal combustion engine, which is associated with a converter bridge with triggerable switch elements controlled by a regulating device.
2. Description of the Related Art
Claw pole generators are used in motor vehicles to furnish the electrical energy for the on-board vehicle electrical system. These rotary current generators are connected to the direct voltage system of the vehicle via a diode rectifier bridge. The generator outputs power as soon as its induced voltage exceeds the system voltage. The power output of the generator is regulated via the intensity of the exciter current. The system voltage or the output voltage of the generator is typically used as the controlled variable.
To reduce fuel consumption in recent motor vehicles, the idling rpm of the engine is kept as low as possible. A low engine rpm also affects the generator rpm, since the generator is driven by the engine. To allow the generator to output enough electrical energy to the on-board electrical system even during engine idling and to enable recharging of the battery, the generator is required to furnish energy, even at low generator rpm levels. Furthermore, at typical rpm levels the generator should output as much energy as possible. Optimal generator regulation should therefore, on the one hand, make a general power increase possible and, on the other, make it possible to lower the startup rpm, that is, to lower the rpm level above which the rpm can output power.
A rotary current generator for a motor vehicle that outputs improved outset power compared with conventional generators is known from European Patent Disclosure EP 0 762 596 A1. Instead of a conventional rectifier bridge, this rotary current generator has a full-wave-controlled rectifier bridge that includes six controlled switches. By suitable triggering of the switches of the bridge, which for instance include switchable semiconductor elements, phase regulation can be performed in which the phase voltages of the generator are shifted relative to the phase currents. As a consequence, additional currents flow into the stator windings and lead to an increase in the starting power of the rotary current generator compared to a rotary current generator with only a simple diode bridge.
It is an object of the present invention to provide an improved method of regulating a generator, especially a claw pole generator driven by an internal combustion engine.
According to the invention the method for controlling or regulating a generator, said generator having three stator windings and respective generator terminals associated with the windings, a converter bridge including controllable switch elements and means for controlling the switch elements, includes temporarily connecting the stator windings for a predetermined time interval with a charge source that supplies a charging current to the stator windings in addition to induced current present in the stator windings, which charges a generator inductance with magnetic energy from the charge source. The charge source is either a battery or a capacitor.
The method of the invention for regulating a generator has the advantage that the generator furnishes a higher starting power, and that in particular at low rpm it furnishes a higher starting power. It is especially advantageous that the so-called startup rpm of the generator, that is, the rpm above which it is at all possible to output power, is lowered compared with conventional generators.
The method of the invention can be employed to obtain the above objectives and advantages, since a converter bridge with switch elements instead of conventional diodes is associated with the generator. By the correct triggering of these switch elements, it is possible to connect the generator terminals to the positive or negative pole of the battery independently of the natural ignition times of a diode bridge. By suitable triggering of the switch elements, additional currents are supplied to the generator terminals, and the output power of the generator can be increased. These additional currents are initially drawn from the battery, or optionally from an intermediate circuit capacitor, and delivered to the generator via the switch elements. The feeding times into the generator phases are advantageously selected so that they are located in intervals in which the phase current in diode operation is low or disappears (ripples). The power increase of the generator because of the direct current pulsation is associated with an increased waviness of the output current. This waviness is composed of the generator output current and the withdrawal of the current pulses. Advantageously, however, smoothing can again be attained with the aid of an additional capacitor.